THE WEATHER AND INFLUENZA
Some remarkable facts have been deduced by the late Dr. L. Gillespie,
Medical Registrar, from the records of the Royal Infirmary of Edinburgh.
He considered that it might lead to interesting results if the admissions
into the medical wards were contrasted with the varying states of the
atmosphere. The repeated attacks of influenza made him pay particular
attention to the influence of the weather on that disease.
The meteorological facts taken comprise the weekly type of weather, _i.e._
cyclonic or anti-cyclonic, the extremes of temperature for the district
for each week, and the mean weekly rainfall for the same district. More
use is made of the extremes than of the mean, for rapid changes of
temperature have a greater influence on disease than the actual mean.
The period which he took up comprises the seven years 1888-1895. There was
a yearly average of admissions of 3938; so that he had a good field for
observation. Six distinct epidemics of influenza, varying in intensity,
occurred during that period; yet there had been only twenty-three attacks
between 1510 and 1890. Accordingly, these six epidemics must have had a
great influence on the incidence of disease in the same period, knowing
the vigorous action of the poison on the respiratory, the circulatory, and
the nervous systems. The epidemics of influenza recorded in this country
have usually occurred during the winter months.
The first epidemic, which began on the 15th of December 1889 and continued
for nine weeks, was preceded by six weeks of cyclonic weather, which was
not, however, accompanied by a heavy rainfall. Throughout the course of
the disease, the type continued to be almost exclusively cyclonic, with a
heavy rainfall, a high temperature, and a great deficiency of sunshine.
The four weeks immediately following were also chiefly cyclonic, but with
a smaller rainfall.
The summer epidemic of 1891 followed a fine winter and spring, during
which anti-cyclonic conditions were largely prevalent. But the epidemic
was immediately preceded by wet weather and a low barometer. It took place
in dry weather, and was followed by wet, cyclonic weather in turn.
The great winter epidemic of 1891 followed an extremely wet and broken
autumn. Simultaneously with the establishment of an anti-cyclone, with
east wind, practically no rain, and a lowering temperature, the influenza
commenced. Great extremes in the temperature followed, the advent of
warmer weather and more equable days witnessing the disappearance of the
disease.
The fourth epidemic was preceded by a wet period, ushered in by dry
weather, accompanied by great heat; and its close occurred in slightly
wetter weather, but under anti-cyclonic conditions. The fifth outbreak
began after a short anti-cyclone had become established over our islands,
continued during a long spell of cyclonic weather with a considerable
rainfall, but was drowned out by heavy rains. The last appearance of the
modern plague, of which Dr. Gillespie's paper treats, commenced after cold
and wet weather, continued in very cold but drier weather, and subsided in
warmth with a moderate rainfall.
The conditions of these six epidemics were very variable in some respects,
and regular in others. The most constant condition was the decreased
rainfall at the time, when the disease was becoming epidemic.
Anti-cyclonic weather prevailed at the time.
According to Dr. Gillespie, the tables seem to suggest that a type of
weather, which is liable to cause catarrhs and other affections of the
respiratory tract, precedes the attacks of influenza; but that the
occurrence of influenza in _epidemic form_ does not appear to take place
until another and drier type has been established. As the weather changes,
the affected patients increase with a rush.
He is of opinion that the supposed rapid spread of influenza on the
establishment of anti-cyclonic conditions may be explained in this way.
The air in the cyclonic vortex, drawn chiefly from the atmosphere over the
ocean, is moist, and contains none of the contagion; the air of the
anti-cyclone, derived from the higher strata, and thus from distant
cyclones, descending, blows gently over the land to the nearest cyclone,
and, being drier, is more able to carry suspended particles with it. He
considers that temperature has nothing to do with the problem, except in
so far as the different types of weather may modify it. The Infirmary
records point to the occurrence of similar phenomena, recorded on previous
occasions. Accordingly, if such meteorological conditions are not
indispensable to the spread of influenza in epidemic form, they at least
afford favourable facilities for it.